1. Field
This patent specification relates to an information record and playback apparatus in use for information recording media such as optical disks, magneto-optical disks and other similar media, and more particularly, to a demodulation circuit in such apparatus configured to carry out address demodulation.
2. Discussion of the Background
In data recording media such as optical disks, for example, it has been known to provide data prefabricated on the disk and include address information utilized for specifying the position for recording data, and information such as synchronization signals and wobbling signals for controlling the disk rotation, and other similar data.
As optical recording media capable of additionally writing (or recording) information data on the basis of these pre-data, also known previously are CD-recordable (CD-R) disks which have the approximately same storage capacity as compact disks (CDs).
The pre-data are in general prepared by forming in advance recording tracks such as grooves and lands for recording information data, in which the pre-data to be recorded are first frequency modulated (FM) to obtains FM signals. Subsequently, the pre-data to be recorded are incorporated into the disk by forming recording tracks to have a wobbling surface with the wobbling frequency corresponding to the FM signal frequency.
In order to additionally record information data into the CD-R disks, a playback apparatus detects wobbling signals from the wobbling pattern on the disk to obtain a wobbling frequency, then extracts standard clock signals for controlling the disk rotation on the basis of the wobbling frequency. In addition, the apparatus generates necessary drive signals for controlling the rotation of a spindle motor in use for the CD-R disk rotation, then generates recording clock signals including timing signals in synchronous with the CD-R disk rotation.
Also in the CD-R disks, address information on the disks needed for information data recording is obtained by first playing back the pre-data during the data recording and subsequently detecting the position to record on the basis of the pre-data, to thereby be able to achieve the recording.
High density recording media have also been put into practical use recently, such as digital video disks or digital versatile disks (DVDs), which has an increased storage capacity over the previous CDs.
Among the higher density storage media exemplified by the DVDs, information data tracks (e.g., grooved tracks) are formed, having the aforementioned wobbling surface on the basis of the frequency corresponding to standard clock signals. This method is used in optical recording media such as write once type DVD recordable (DVD-R) and DVD Rewritable (DVD+RW) media.
Regarding error correction for the pre-data recorded into the DVD-R and DVD+RW disks, it is necessary to add a plurality of data to be utilized in the error correction, since the position and pattern of an error have to be computed. The error correction data are typically exemplified by the Reed-Solomon code which has been in use for not only DVD disks but also CDs and digital audio tapes (DATs).
As the data to be added for the error correction using the Reed-Solomon code, parity words consisting of at least 2t words are necessary for correcting an error of t words.
For example, for land prepit data (which is hereinafter referred to as xe2x80x98LPPxe2x80x99), a parity word consisting of three words is added to an address information data of three words, and one oneword error in the address information can be corrected. In contrast, for the case of address data in pre-groove (which is hereinafter referred to as xe2x80x98ADIPxe2x80x99), a five-words parity word is added to an eight-words address multiplex (MUX) information data, and one two-words error in the address MUX information can be corrected.
As described above, in error correction steps for the address data played back from the DVD type disks, there have previously persisted drawbacks such as low efficiency in the error correction, for example, in which the number of words which is successfully corrected is relatively small compared with the number of added parity words.
Accordingly, it is an object of the present disclosure to provide an information record and playback apparatus, having most, if not all, of the advantages and features of similar employed apparatuses, while eliminating many of the aforementioned disadvantages.
It is another object of the present disclosure to provide an information record and playback apparatus which is capable of achieving improved efficiency in error correction for DVD type optical disks.
The following brief description is a synopsis of only selected features and attributes of the present disclosure. A more complete description thereof is found below in the section entitled xe2x80x9cDescription of the Preferred Embodimentsxe2x80x9d
An information record and playback apparatus disclosed herein is configured to perform record and playback operations of an optical disk which is provided with data recording tracks having the surface wobbled at a predetermined frequency and a plurality of prepits formed on the surface with a predetermined phase relation to the position for data recording.
The apparatus includes a preset signal generation unit configured to detect the prepits, and generate and output prepit signals; a data decoding circuit configured to decode the prepit signals, and extract decoded information data; a data error detection unit configured to compare the pattern of information data to that of a predetermined data, and output the decoded information data added with a predetermined error flag, if both of the patterns are not in coincidence each other; and a data error correction unit configured to compute the position of an error on the basis of the error flag and provide error correction to the decoded information data.
The data error correction unit is configured to carry out erasure correction with the Reed-Solomon code prior to error correction of the decoded information data. In addition, the data error correction unit carries out the detection of the position of, and the correction of, error data bits using only data bits demodulated by the data demodulation unit if a number of error flags that is added by the data error detection unit exceeds a predetermined number.
In another aspect disclosed herein, an information record and playback apparatus is configured to perform record and playback operations of an optical disk which is provided with data recording tracks having the surface wobbled so as to be capable of indicating information data by phase inversion according to the dual phase modulation method.
The apparatus includes a wobbling signal generation unit configured to detect wobbling components previously recorded on the data recording track and generate wobbling signals; a data decoding unit configured to phase-demodulate the wobbling signals and extract decoded information data; a data error detection unit configured to integrate the decoded information data for each pattern of the data, compare a data pattern of the decoded information data with a predetermined value to obtain a comparison result, detect an error for the data pattern on the basis of the comparison result, and output the data pattern added with a predetermined error flag; and a data error correction unit configured to compute the position of the error on the basis of an error flag to subsequently provide error correction to the decoded information data.
The data error correction unit is configured to carry out inversion processing of the decoded information data when the decoded information data form a predetermined data pattern, such that the integration value of data pattern reaches either a maximum value or a minimum value, and output the data pattern added with a predetermined error flag if a resultant integration value of the data pattern is obtained between the maximum and minimum values.
In addition, the data error correction unit is configured to carry out erasure correction with the Reed-Solomon code prior to error correction of the decoded information data. Further, the data error correction unit is configured to carry out the detection of the position of, and the correction of error data bits using only data bits demodulated by the data demodulation unit if a number of error flags that is added by the data error detection unit exceeds a predetermined number.